CVE-2007-4657 in PHP
Summary
by MITRE
Multiple integer overflows in PHP 4 before 4.4.8, and PHP 5 before 5.2.4, allow remote attackers to obtain sensitive information (memory contents) or cause a denial of service (thread crash) via a large len value to the (1) strspn or (2) strcspn function, which triggers an out-of-bounds read. NOTE: this affects different product versions than CVE-2007-3996.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability described in CVE-2007-4657 represents a critical security flaw affecting PHP versions prior to 4.4.8 and 5.2.4, where multiple integer overflows occur in the strspn and strcspn functions. These functions are commonly used for string manipulation operations, specifically for counting characters that match or do not match a given set of characters. The flaw manifests when a large len parameter value is passed to these functions, causing integer overflow conditions that result in unpredictable behavior. This vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, which is a well-documented weakness in software development where arithmetic operations exceed the maximum value that can be represented by the data type.
The technical implementation of this vulnerability exploits the way PHP handles integer arithmetic when processing string functions. When the len parameter exceeds the maximum value that can be stored in the integer data type, the overflow causes the system to interpret the result as a negative number or a value that wraps around to a much smaller number. This leads to memory access violations where the application attempts to read from memory locations that are outside the bounds of the allocated buffer. The out-of-bounds read operation can expose sensitive memory contents to attackers, potentially revealing system information, credentials, or other confidential data that should remain protected. Additionally, the overflow can cause the application thread to crash, leading to denial of service conditions that disrupt legitimate user access to the web application.
From an operational perspective, this vulnerability poses significant risks to web applications running on affected PHP versions, as it can be exploited remotely without requiring authentication or special privileges. Attackers can craft malicious requests containing oversized len parameters to trigger the integer overflow conditions in strspn and strcspn functions, potentially leading to information disclosure or service disruption. The vulnerability is particularly dangerous because it affects core string manipulation functions that are frequently used in web applications, making it a prime target for exploitation. According to ATT&CK framework, this vulnerability maps to T1059.007 (Command and Scripting Interpreter: PowerShell) and T1499.004 (Network Denial of Service) techniques, as it enables both information gathering and service disruption capabilities. The impact extends beyond simple denial of service, as the memory disclosure aspect can provide attackers with sensitive information that may be used for further exploitation attempts.
The recommended mitigation strategy involves immediate patching of affected PHP installations to versions 4.4.8 or 5.2.4, which contain the necessary fixes for the integer overflow conditions. Organizations should also implement proper input validation and sanitization measures to prevent malicious len parameter values from reaching the vulnerable functions. Security monitoring should include detection of unusual string processing patterns that might indicate exploitation attempts, while network segmentation and access controls can limit the potential impact of successful attacks. Additionally, regular security assessments and vulnerability scanning should be conducted to identify any other instances of similar integer overflow issues within the application stack, as these vulnerabilities often indicate broader coding practices that may contain other security weaknesses.